One of the prior types of systems for lifting vehicles for repair is a system in which the synchronous movement of vehicle supports of a pair of jacks is effected by conduits connecting together, in series, hydraulic cylinders provided for the respective jacks and a source of hydraulic fluid to actuate the cylinders.
In the manufacture of the foregoing system of the prior art, the work of connecting together the cylindres and the fluid source in series takes much time and trouble and requires a highly-developed piping technique. Also, if air is contained in the conduits or the cylinders or if the fluid leaks therefrom, the exact synchronous movement of the jacks and, hence, of their vehicle supports may be lost. In such a case, a vehicle on the supports may have a tilt and fall down. Therefore, such a situation may constitute a grave danger. Thus the foregoing prior system may require a vigorous inspection thereof at frequent intervals.